Fixing station for fixing toner images on a supporting material with a mobile covering device

ABSTRACT

A fixing station for a printer or copier includes a heating device for fusing toner to the carrier material and a cover that is selectively insertable between the heating element and the carrier material. The cover may be a window blind type cover. Where two sided fixing is provided, both heating devices have a cover. The cover may have an energy storage spring to cause the heating device to be covered in the event of an emergency. An electro-magnetic locking device may be provided to retain the cover in an open position.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a fixing station for fixing tonerimages on a carrier material, having a heating device with at least oneradiant heat source that emits radiation in the direction of the carriermaterial, and having a cover device with which an undesired incidence ofradiation onto the carrier material can be prevented.

2. Description of the Related Art

In electrographic printers or copiers, the toner image transferred froman intermediate carrier, generally a photoconductor, onto the carriermaterial, generally paper, must be fixed, i.e. it must be joined so asto be smear-proof and abrasion-proof to the carrier material.Heat/pressure fixing is currently usually utilized inelectrophotography. When no pre-heating, for example with the assistanceof a heating saddle, of the carrier material is undertaken, this isusually limited to approximately 0.5 m/s through 0.7 m/s in terms ofprocessing speed. In the duplex printing mode wherein the front side andthe back side of a carrier material are printed, the fixing process isrelatively difficult because both sides are still covered with smearabletoner images. A high fixing quality given simultaneous fixing of thefront side and of the back side of the carrier material can only beachieved with relatively soft fixing drums, for example silicone drums.These fixing drums have a low service life and are uneconomical. Suchsoft fixing drums are therefore only utilized given printers having arelative low printing volume. Since soft fixing drums are utilized atboth sides of the carrier material, the guidance of the carrier materialbecomes problematical. Such fixing drums are therefore not suited in thefurther-processing of continuous form paper.

For said reasons, it is desirable to fix toner images contact-free,whereby a relatively broad spectrum of carrier material can be utilized.Another goal of contact-free fixing is comprised in achieving a highfixing quality without smearing effects.

A contact-free fixing method is known wherein the toner material issoftened with the assistance of a solvent material, so that it unitesbetter with the fibers of the carrier material. When, however, chromatictoner is employed, it can occur that the color pigments are dissolved todifferent extents, which can potentially lead to a color-dependentsmearing of the toner images. Moreover, the known environmental problemsgiven the utilization of solvents arise.

Another known fixing method that works contact-free is what is referredto as photoflash fixing, whereby the toner is fixed on the carriermaterial with the assistance of high-energy light pulses. The wavelengthof the radiation usually lies in the visible through ultraviolet rangeof the spectrum. Since the various color toners absorb to differentextents in this wavelength range, a photoflash fixing is not suitablefor multi-color printing.

Another fixing station is disclosed by European Patent Document EP-A-0629 930. The fixing station is employed for an electrostatic printer inorder to fix toner material on paper. The cover device serves thepurpose of preventing the incidence of radiation during a heating-upphase or during a standstill of the carrier material. In the closedcondition of the cover device, the active surfaces of the radiant heatsource emitting thermal radiation face away from the carrier material.In this condition, the cover device surrounds the radiant heat source,so that the heating-up phase is shortened. During normal operationwherein the toner material is fixed on the carrier material as aconsequence of the incident radiant heat, the radiant heat source facestoward the carrier material and the radiation can impinge the carriermaterial unimpeded.

Japanese Patent Document JP-A-62-055685 discloses a fixing devicewherein a cover device can be moved into the beam path between a radiantheat source and a carrier material. The cover device comprises a plateof heat-resistant material. The cover device is removed from the beampath in the normal operating condition. Given an abnormal operatingcondition, the cover plate is shoved between the carrier material andradiant heat source.

The Japanese Patent document JP-A-60-014268 is directed to a fixingdevice wherein a cover plate can be moved into the beam path between aradiant heat source and a carrier material. The intensity of the fixingis set with the assistance of this cover plate dependent on the paperthickness of the carrier material. A detector thereby determines thepaper thickness, whereupon the cover plate is swivelled. The fixingdevice can be set to different paper thicknesses relatively fast in thisway.

SUMMARY OF THE INVENTION

An object of the invention is to provide a fixing station that workswith high processing speed and assures a high print quality.

This object is achieved by a fixing station for fixing toner images on acarrier material, including a heating device with at least one radiantheat source that emits radiation in the direction of the carriermaterial, and having a cover device movable essentially parallel to themoving direction of the carrier material and that can be moved in to thebeam path between radiant heat source and carrier material, in that,given a stop of the carrier material, the cover device is moved with thevelocity V_(R), according to the relationship: V_(R)=−V_(P), wherein vpis the transport velocity of the carrier material; and in that, givencontinued transport of the carrier material with the velocity V_(P), thecover device is moved with the velocity V_(R), according to therelationship: V_(R)=V_(P). Advantageous developments provided by thecover device having at least the width of the carrier material.Specifically, the cover device is flexible as viewed in moving directionof the carrier material. In one embodiment, the cover device contains aband. Alternately, the cover device contains a plurality of strip-shapedlamellae that form a window blind, whereby adjoining lamellae preferablyoverlap. The band or, respectively, the lamellae can be wound up in thefashion of a winding.

In a preferred embodiment, an endless deflection means is arrangedaround the heating device; and the band or, respectively, the windowblind can be moved along the deflection device. The deflection devicemay contain a tensing mechanism that keeps the band or, respectively,the window blind in a tensed condition. A feature of the inventionprovides that the cover device has a length that is adequate in order tocover the entire radiation of the radiant heat source in the directionof the carrier material. The cover device may contain a rigid plate forcovering the radiation.

The fixing station of one embodiment has a radiant heat source with aradiation temperature in the range from 500° C. through 800° C. and themaximum intensity of the radiation lies at a wavelength greater than 2μm. In one embodiment, a respective heating device each having at leastone radiant heat source is arranged at both sides of the carriermaterial, whereby a respective cover device can be moved into the beampath between radiant heat source and carrier material, whereby bothcover devices are preferably moved by a common drive. Such a fixingstation may be employed for a printer device or copier device that worksin duplex printing mode.

A ceramic flat radiator, a crystal radiator or, in particular, a foilradiator can be employed as the radiant heat source. In one aspect ofthe invention, the radiant heat source is pre-heated. Specifically, theradiant heat source is pre-heated to a temperature above 200° C.

Advantages of the invention are realized when a temperature Tm isestablished in the steady state at the carrier material given anoperation of the radiant heat source with nominal power NL; and theradiant heat source is preheated such that a temperature ofapproximately 0.45 Tm is established on the carrier material. A furtherfeature of the invention is that a temperature sensor acquires thetemperature on the carrier material, preferably when it departs thefixing station; and the energy supplied to the radiant heat source isset such that it lies slightly above the fixing temperature Tf. Thefixing temperature amounts to, for example, 0.8×Tm.

A feature of the invention provides that a power control is providedthat supplies electrical energy to the radiant heat source; in theoperating condition with constant printing, the power control sets apower of approximately 80% NL, whereby NL is the nominal power; in theoperating condition with short stoppage of less than 10 seconds, thepower is to set to 60% through 80% NL; given an operating condition withlong stoppage of >10 seconds through <5 minutes, a power of 30% through60% NL is set; in the operating condition of standby mode having awaiting time of >5 minutes, a power of less than 30% NL is set; andgiven the start operating condition, a power of 100% NL is set.

Each radiant heat source is divided to a plurality of zones that arerespectively separately supplied with the electrical energy; and thezones are supplied with electrical energy dependent on the width of thecarrier material. As a preferred development, zones opposite which nocarrier material resides are driven with reduced power. In one example,a longitudinal edge of the carrier material lies within a zone. Further,a plurality of zones are combined and driven like a single zone. Inembodiments having two heating devices, zones residing opposite oneanother are driven with the same power. The zones residing opposite oneanother may be connected in series. As a further aspect, the powercontrol ensues with a pulse packet control or a phase control.

A temperature regulation ensues such that a temperature higher than thefixing temperature is set in zones having carrier material and a lowertemperature is set in zones without carrier material. A temperatureregulation ensues only in zones with carrier material.

The cover device may be connected to a safety mechanism that contains anenergy store; and, given outage of the drive for the cover device,energy is taken from the energy store with which the cover device ismoved by the safety mechanism into the beam path between radiationsource and carrier material. In an exemplary embodiment, the energystore is a spring energy store that preferably contains a linear spring,a rotatory spring or a gas spring. The energy store is filled withenergy given every closing movement of the cover device, or alternately,the energy store is filled once with energy by a drive of the coverdevice and is subsequently locked by a locking mechanism; and thelocking is released given outage of the drive. The locking mechanism maycontain an electromagnet that is permeated by current during normaloperation; and the lock is released given outage of the current anddrop-off of the electromagnet. The drive for the cover device maycontain a magnetic coupling that uncouples the drive given outage of thedrive.

Shock absorbers that damp the impact of the cover devices are containedin the heating devices.

The traction means is conducted over a deflection roller.

The locking mechanism contains a swivel lever with an oblong hole guide;the retainer magnet holds the swivel lever at its projecting end; across pin of the deflection roller is guided in a stationarylongitudinal guide and in the oblong hole guide; given a drop-off of theretaining magnet, the swivel lever is turned until oblong hole guide andlongitudinal guide are aligned with one another and the cross pin movesin both guides.

According to the invention, the heating device contains a radiant heatsource as a result whereof the fixing procedure ensues contact-free.Problems related to the guidance and the pressure charging of fixingdrums are thus avoided. The employment of a radiant heat source,however, has the disadvantage that the heating of the cooling of thecarrier material involves a relatively high time constant, as a resultwhereof problems arise when starting printing, given standstill of thecarrier material or given intermittent printing. According to theinvention, a cover device is proposed that can be moved into the beampath between radiation source and carrier material or given intermittentprinting. According to the invention, a cover device is proposed thatcan be moved into the beam path between radiation source and carriermaterial. With the assistance of this cover device, defined exposuretime for achieving an optimum fixing can be achieved even given frequentstarting and stopping of the movement of the carrier material. Due tothe contact-free heating of the carrier, a high color reproducibilityand uniformity of the fixing of the toner image can be achieved.

The fixing station is preferably employed for a printer device or copierdevice having high printing performance that works in duplex printingmode, whereby toner images of the front side and of the back side of thecarrier material are simultaneously fixed. In this operating mode,heating devices and corresponding cover devices are provided at bothsides of the carrier material.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are explained below withreference to the drawing.

FIG. 1 is a schematic longitudinal section through a fixing stationhaving a cover device in the fashion of a window blind;

FIG. 2 is a cross-section through the fixing.station of FIG. 1;

FIG. 3 is a band-shape cover device;

FIG. 4 is a cover device in the fashion of a window blind havingstrip-shaped lamellae;

FIG. 5 is a graph showing the power supply to the heating device via theon-time in the operating modes of cold start and warm start;

FIG. 6 is a diagram for illustrating the control of the heating power;

FIG. 7 is the tabular allocation of the supplied power dependent on theoperating condition;

FIG. 8 is a block circuit diagram of the power control for the radiantheat source;

FIG. 9 is a perspective view which shows schematically, the arrangementof two heating devices at both sides of the carrier material;

FIG. 10 is a schematic representation of the division of the heatingdevice into various zones;

FIG. 11 is a circuit diagram which shows schematically, the drive ofdifferent zones;

FIG. 12 is a side sectional view of an exemplary embodiment of a safetymeans having a spring store;

FIG. 13 is a status table for normal operation and given the occurrenceof a malfunction;

FIG. 14 is a side cross section of a safety device having an interlockelement;

FIG. 15 is a side cross section of a similar exemplary embodiment havinga gas compression spring;

FIG. 16 is a status table for normal operation and given malfunction;

FIG. 17 is a side cross section of an exemplary embodiment for atraction means guidance having two tension springs;

FIG. 18 is a side cross section of a simple arrangement of the tractionmeans guidance;

FIG. 19 is a top perspective view of an exemplary embodiment of acombination composed of locking latch and retaining magnet;

FIG. 20 is a top perspective view of an embodiment of the interlockhaving a linear movement of the locking latch;

FIG. 21 is an end perspective view of an interlock mechanism having aswivel lever; and

FIG. 22 is a side view of an exemplary embodiment having swivel leverand entrained tension spring.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a longitudinal section through a fixing station of theinvention. This fixing station is utilized in a high-performance printerthat prints a paper web 10 double-sided. In the illustration of FIG. 1,only the upper part of the fixing station is shown, this charging theupper side of the carrier material with thermal energy for fixing tonerimages. An identical apparatus (not shown) is provided at the undersideof the paper web 10, toner images on the underside being fixedtherewith. The fixing station contains a radiant heat source 12 that isfashioned as a foil radiator. Such a foil radiator has 50 μm thick bandsthat assume a temperature <800 ° C. when charged with current. Theadvantage of a foil radiator is comprised therein that it has a lowthermal capacity and can thus be quickly heated and just as quicklycooled. Other radiant heat sources that can be employed are ceramic flatradiators wherein the heating coil is embedded in ceramic compound.Likewise, crystal radiation sources can be employed wherein the globecoil is installed in crystal tubes.

An insulation 14 that has a downward opening for the emergence of theradiant heat is provided around the radiant heat source 12. A coverdevice 16 that can be moved into the beam path between the radiationsource 12 and the paper web lO is arranged between the radiant heatsource 12 and the paper web 10. In the present case, the cover device 16contains strip-shaped lamellae that are combined in the fashion of awindow blind 16. The cover device 16 is thus flexible as viewed in themoving direction of the paper web 10 and can be deflected at deflectionrollers 18. One of the deflection rollers 18, for example that shown atthe lower right in FIG. 1, is driven by a drive. The strip-shapedlamellae that form the window blind 16 are tensed between twocirculating toothed belts 20 (only one toothed belt 20 can be seen inFIG. 1). Due to forward or backward movement of the toothed belt 20, thewindow blind 16 can be moved into the beam path between the radiationsource 12 and the paper web 10 in order to thus shield thermal radiationfrom impinging the paper web 10. The length of the window blind 16 isdimensioned such that, in its closed condition, it covers the entireradiation-emitting region of the radiant heat source 12. Alternatively,to the toothed belt 20, two wire cables or chains can also be employed.

The transport mechanism with the toothed belt or wire cable drive islocated at both sides outside the emission region of the radiant heatsource 12. The deflection means formed by the deflection rollers 18 isthus compact and occupies little space.

The cover device 16 is exposed to relatively great temperaturedifferences. In the opened condition, room temperature is approximatelypresent; in the closed condition, the cover device 16 can assume atemperature of up to approximately 600 ° C. As a result of the lengthchanges due to the temperature differences, a clamp mechanism isprovided at at least one deflection roller 18 (this clamp mechanism notbeing shown). This clamp mechanism generates a constant tension in thetoothed belt 20, so that the window blind 16 is also tensed. The clampmechanism can be realized, for example, with a belt tensioning meanshaving a durably applied spring tension. In order to intercept a changein length transversely relative to the paper web 10 due to temperaturedifferences, the deflection rollers 18 are arranged axially adjustable.

FIG. 2 shows a cross-section through the arrangement of FIG. 1, wherebythe window blind 16 is in its closed position. The deflection rollers 18are occupied with the circulating toothed belt 20 at the left in FIG. 2.The toothed belt 20 has been omitted at the right side.

FIG. 3 shows an exemplary embodiment of the cover device 16′ realized asa flexible band.

FIG. 4 shows the stripe-shaped lamellae that, overall, form the windowblind 16. The individual lamellae are composed of highlytemperature-resistant material, for example sheet steel, having atypical thickness of 0.1 through 0.3 mm. Materials in the form of bandsor plates or fabric having low thermal conduction such as, for example,glass fibers, silicate fibers or ceramic fiber paper can also beemployed, these assuring an optimally low thermal load on the paper web10 in the closed condition. For stabilization, the lamellae can beapplied on a temperature-resistant, tear-resistant supporting grid. Theaforementioned fiber products can also be employed together with metal;the fiber products then serve for additional heat damming.

An embodiment is also conceivable wherein the flexible band or,respectively, the lamellae can be wound up in the fashion of a winding,i.e. the closed deflection device shown in FIG. 1 is replaced by atake-up reel and an unwinding reel on which the window blind or,respectively, the band is rolled up and from which it is unrolled.

The lamellae can be formed of relatively inflexible material, forexample of ceramic or of hollow profiles of steel. Such hollow profiles,which can in turn be composed of U-profiles, are preferably flooded withair for cooling.

The movement of the cover device is dependent on the operating conditionof the paper web 10. When the paper web 10 stops, the cover device 16 isclosed with the velocity V_(R) according to the relationshipV_(R)=−V_(P), wherein V_(P) denotes the transport velocity of the paperweb 10. This means that the fixing event, even given a sudden standstillof the paper web 10 due, for example, to a paper jam or due to anoperationally caused stopping of the paper web 10, is still maintainedfor the section of the paper web located under the radiant heat source12 for a length of time during which it would have been charged withradiant heat given normal further-transport. The section located underthe radiant heat source 12 is thus still adequately exposed in order tofix the toner images, despite the stopping of the paper web 10.

Given further transport of the paper web 10 with the velocity V_(P), thecover device is opened in the same direction with the velocity V_(R).The relationship V_(R)=V_(P) thus applies. What is thus achieved is thatthe new section of the paper web 10 coming under the radiant heat source12 is charged with the correct dose of radiant heat. The precedingsection of the paper web 10 is not overexposed.

The cover devices 16 shown in FIGS. 1 through 4 are flexible. In analternative embodiment, however, it is also possible to employ a rigidplate that can be moved as needed into the beam path between the radiantheat source 12 and carrier material 10 with a drive mechanism.

The radiant heat source 12 has a preferred radiation temperature in therange from 500° C. through 800° C. Its maximum radiant intensity lies ata wavelength >2 μm.

When printing in an electrographic printer, what are referred to asstart/stop events occur from the greatest variety of reasons, the papertransport having to be halted fork certain time therein; for example,given an interruption of the electronic data stream, given the necessityfor cleaning events in the printing unit or given specific papertransport movements. Since the radiant heat sources that are employedhave a relatively high time constant when heating up, one must wait fora relatively long time given a continued transport of the paper web 10until the fixing station is again ready to be used in order to fix tonerimages with high quality. On the other hand, it can be meaningful whenhalting the paper transport to reduce the energy supply in order toavoid an unnecessary heating of the fixing station and of the paper web.Accordingly, it is desirable to achieve an optimally fast heating givenminimum power consumption.

FIG. 5 shows a diagram of the typical heating behavior of a paper web inthe steady state, i.e. a radiant heat source is permanently operatedwith nominal power NL, as a result whereof a maximum paper temperatureTm that is recited as 100% occurs. This maximum paper temperature Tm isonly achieved after a time of eight minutes. Typically, the papertemperature then amounts to 180° C. A fixing of the toner is onlyachieved above a fixing limit at a fixing temperature Tf. It typicallyamounts to 80% of the maximum temperature Tm. The time until the fixinglimit is reached typically amounts to 1 through 3 minutes when heatingis carried out proceeding from room temperature. Such an operatingcondition is referred to as cold start. Except when switching theprinter on, such a time is unacceptable for a fast printing mode.

When the radiant heat source is permanently held at a temperature thatlies clearly above room temperature, for example above 200° C., then theheating-up time until the fixing limit is reached can be considerablyshortened. FIG. 5 shows a curve referred to as warm start wherein theenergy supplied to the radiant heat source is set such that the paperheats to approximately 45% of the obtainable final temperature. When thefixing station is then to begin its normal operation, the radiant heatsource is operated with nominal power NL, whereby the fixing limit withfixing temperature Tf is reached within ten seconds. At the same time,the power with which the radiant heat source is driven is clearlyreduced in faces wherein printing mode does not ensue. For example, thispower then amount to only 40% of the nominal power NL.

The radiant heat source is operated with nominal power NL until thefixing limit is reached. After the fixing limit is reached, the power isset such that the temperature of the paper at the end of the fixingstation, i.e. in regions of the paper that leave the fixing station,lies slightly above the fixing temperature Tf. Due to this type ofregulation of the paper output temperature, one is largely independentof the material employed; in particular, this procedure is independentof the paper weight.

In a diagram similar to that of FIG. 5, FIG. 6 shows the papertemperature over time. Due to the pre-heating, the fixing limit isquickly exceeded. Subsequently, the regulation sees to it that the papertemperature lies slightly above the fixing limit when leaving the fixingstation.

FIG. 7 shows the selected power for the radiant heat source dependent onthe operating condition. In the operating condition of “continuousprinting”, the power supplied to the radiant heat source amounts toapproximately 80% of the nominal power NL. In the operating conditionwith brief stoppage of the paper web, the power amounts to approximately60 through 80% of the nominal power NL. In the operating condition withlonger stoppage of the paper web, for example <5 minutes, the poweramounts to 30 through 60% of the nominal power NL. In standby mode,given a stoppage of the paper web for longer than 5 minutes, the poweramounts to less than 30% of the nominal power NL. Given continuedtransport of the paper web following a pause, the supplied power amountsto 100% of the nominal power NL.

FIG. 8 shows the schematic block illustration of the control of theradiant heat source that has different power stages 1 . . . N. Thesepower stages are dependent on said operating conditions 1 . . . N of theprinter. The temperature of the paper web at the output of the fixingstation serves as regulating variable.

FIG. 9 schematically shows an arrangement for a fixing station asemployed in duplex printing mode. The paper web 10 is irradiated by anupper radiant heat source 12 a and by a lower radiant heat source 12 bin order to fix toner images on both sides of the paper web 10. Eachradiant heat source contains a plurality of zones Z1 through Z6 (seeFIG. 10) that can be respectively driven independently of one another.For example, the various zones Z1 through Z6 are realized by heatingfoils whose connections are separately conducted out.

A fixing station must be able to process paper webs having differentwidths. It is required for a high fixing quality that the intensity ofthe irradiation is relatively uniform over the entire width of the paperweb, so that a uniform temperature is established. Given a radiant heatsource, a drop in the radiant intensity occurs toward the edge. On theother hand, an overheating can occur given the arrangement according toFIGS. 1 and 2 and given hot zones residing opposite one another withouta paper web, since no thermal energy is conveyed out by the paper web.In such a case, overheatings can occur at the edge of the paper web,quality deficiencies occurring as a result thereof.

At its left side, the paper web 10 shown in FIG. 10 has a stationarypaper edge; the other paper edge, dependent on the format width, entersinto the radiant heat sources 12 a and 12 b lying opposite one another.In order to compensate for the drop of the radiant intensity in thezones Z1 toward the edge, the edge at the left side is displaced towardthe right. In order to minimize the control outlay for controlling thevarious, independent zones Z1 through Z6, zones Z1 through Z4 whereinthe paper web 10 resides opposite these zones are combined. Each zoneresiding opposite is then driven with the same heating power. When theformat width increases, then individual zones, for example the zone Z5or the zones Z5 and Z6 are connected together.

FIG. 11 shows a circuit arrangement for the drive of the various zonesZ1 through Z6 of the radiant heat sources 12 a and 12 b. In the presentcase, zones Z1 through Z6 residing opposite one another are connected inparallel. However, it is also possible to connect zones residingopposite one another in series, as a result whereof the voltage droppingoff per zone is cut in half. For example, the energy supply can ensuewith a pulse packet control or a phase control. Given the pulse packetcontrol, the zones Z1 through Z6 are supplied with a plurality ofcurrent pulses per time unit that is dependent on the power to be set. Aregulation of the temperature is outlined in FIG. 11. A temperaturesensor 20 acquires the surface temperature of the paper web 10 thatextends along the zones Z1 through Z4. The signal of the sensor 20proceeds to a control unit 22 that supplies the combined zones Z1, Z2,Z3 and Z4 with power such that a constant temperature is set. A secondsensor 24 acquires the temperature in the region wherein no paper web 10resides opposite the zones Z5 and Z6. The signal of the sensor 24 issupplied to a regulator 26 that supplies the combined zones Z5 and Z6with electrical energy such that a lower temperature is set in thesezones Z5 and Z6 than in the zones Z1 through Z4 that emit radiant energyonto the paper web 10. In this way, an overheating is avoided in theedge region of the paper web 10 and a uniform temperature profile overthe width of the paper web 10 is nonetheless achieved.

A switchover means U having a plurality of switches U1 through U6determines how the various zones Z1 through Z6 are combined. Dependenton the width of the paper web 10, switching is carried out between theillustrated positions such that the respective zone Z1 through Z6 isdriven either by the regulator 22 or by the regulator 26. The setting ofthe switches U1 through U6 can, for example, be realized with theassistance of a suitable operating condition hardware. In this way, theentire fixing station with two radiant heat sources 12 a, 12 b dividedinto zones can be regulated by two control circuits. A furthersimplification derives when a direct control of the supplied heat powerensues in the region without paper web 10. The sensor 24 can then beomitted.

As mentioned, the radiant heat sources employed are relatively inert, sothat an overheating of the carrier material can nonetheless occur givena stoppage of the carrier material and a shut-off of the energy supplyto the radiant heat source. This overheating can be so pronounced thatthe carrier material, for example paper, ignites. It must therefore beassured that the cover device functions reliably even given outage ofthe drive motor, for example when the power fails, in order to precludea dangerous situation. One exemplary embodiment of the invention ischaracterized in that the cover device is connected to a safety meansthat contains an energy store, and that, given outage of the drive forthe cover device, energy is taken from the energy store with which thecover device is moved into the beam path between the radiation sourceand the carrier material by the safety device. An electrical, pneumatic,magnetic or a mechanical store can be employed as the energy store.Preferably, mechanical spring energy is stored in the energy store i.e.it contains a linear spring, a rotatory spring or a gas compressionspring.

A simple exemplary embodiment of a safety device is shown in FIG. 12.The entire fixing station 30 contains two heating devices 32 a and 32 bthat heat the paper web 10 at both sides. The respective cover devices16 a and 16 b are moved by toothed belts 20 a and 20 b. The two toothedbelts 20 a and 20 b are driven by a belt or a chain 34 via drive wheelsand shafts, the belt or chain 34 being placed around a drive shaft 36. Amotor engages at the drive shaft 36. A magnetic coupling is connectedbetween the drive shaft 36 and motor, this uncoupling the motor shaftgiven outage of the motor. A wire cable 38 as a traction means is alsoconnected to the drive shaft 36, this in turn being connected to alinear spring 40. At every back and forth motion of the motor shaft inboth rotational senses in order to close or open the cover devices 16 aand 16 b, the spring 40 is tensed and relaxed when the wire cable 38 iswound onto the drive shaft 36. When a power outage occurs and the coverdevices 16 a and 16 b are in their open condition, the motor is releasedfrom the drive shaft 36 via the magnetic coupling and the wire cable 38turns the drive shaft 36 upon relaxation of the spring 40 such that thecover devices 16 a and 16 b completely cover the radiations emitted bythe radiant heat sources 12 a and 12 b. In order to avoid a hard impactof the cover devices 16 a and 16 b on their limit position in such acondition, shock absorbers 42 a and 42 b are provided that absorb theimpact. The elements of spring 40 and wire cable 38 form a safetypull-back. Instead of the wire cable 38, a chain or a toothed belt canalso be employed. FIG. 13 shows a status table for the normal mode andfor a malfunction.

FIGS. 14 and 15 show a further exemplary embodiment, whereby a lockingmechanism is employed. What is achieved with the assistance of thisblocking mechanism is that the spring store is not tensed or relaxedgiven every movement of the cover device. To this end, the spring storewhich has been loaded once is locked in its tensed condition. Thisinterlock is released in case of hazard.

FIG. 14 shows a development of the exemplary embodiment according toFIG. 13. Identical parts are identically referenced. The spring 40 isconnected to the drive shaft 36 via the traction means 38, for example awire cable, a chain or a toothed belt. In order to keep the tractionmeans 38 under tension, a traction means tenser 44 is provided that,under spring load, tenses the traction means 38 during normal operationgiven the back and forth movement of the cover device 16 a and 16 b. Adetent pawl 46 engages into a detent hook 48. The detent pawl 46 isactuated by an electric retaining magnet 50. A damper 52 that damps thespring movement is connected in parallel to the movement of the spring40. Given operation of the safety mechanism, the spring 40 is tensed atthe beginning once with the assistance of the drive shaft 36 and thetraction means 38, potentially with reduced motor speed. The electricretaining magnet 50 holds the detent pawl 46 in the illustratedcondition when the operating voltage is present. When the spring 40 istightened far enough, the detent hook 48 engages into the detent pawl46. The stroke of the spring 40 is matched to the movement of the coverdevices 16 a and 16 b.

Given a malfunction, the motor is automatically uncoupled by themagnetic coupling, so that it does not impede further movement by thesafety mechanism. Given a lack of operating voltage, the electricretaining magnet 50 disconnects and releases the detent pawl 46. Due tothe spring energy stored in the spring 40, the drive shaft 36 is movedin order to bring the cover devices 16 a and 16 b into the closedcondition. The damper 52 is connected directly in parallel to the spring40. The closing motion is thus uniformly damped over the entireactuation path. In particular, this damping is needed so that the safetymechanism does not cause a hard impact even when the cover device 16 aand 16 b is half-opened.

Advantageously, a gas compression spring that represents a combinationof spring store and damping is employed instead of a linear spring 40and a damper 52. A further advantage of employing gas compressionsprings is comprised therein that a sudden failure does not occur.Whereas normal mechanical springs can fail suddenly due to breakage evengiven a correct design, a gas compression spring gradually losesinternal pressure toward the end of its service life due to wear of theseals. By monitoring the force needed for opening or for locking, thegas compression spring can be employed until shortly before a minimuminternal pressure is reached and a necessary placement can then beindicated via the control panel at the printer.

FIG. 15 shows an embodiment upon employment of a gas compression spring54. The movable end of the gas compression spring 54 is connected to adeflection roller 56 via which the traction means 38 is deflected. Inthe illustrated position, the cover device 16 is closed and the gascompression spring 54 is relaxed. A cable is provided as the tractionmeans 38, this being wound onto the drive shaft 36. The drive power ofthe motor need only be designed for the normal actuation of the coverdevices 16 a and 16 b since the gas compression spring 54 need only berarely tensed and a reduced wind-up speed is therefore possible.

FIG. 16 shows a status table for normal operation and given occurrenceof a malfunction upon employment of a lockable safety return.

FIG. 17 shows an example of a traction agent guidance with two tensionsprings 60 and 62 that act at the ends of the traction means 38. ThisFIG. 17 shows the condition “gas compression spring 54 relaxed” and“cover closed”, i.e. before the tightening of the gas compression spring54 actuation of the gas compression spring 54 in case of malfunction.The overall traction means 38 is moved back and forth between twodetents 63 and 64 upon actuation of the cover devices 16 a and 16 b. Thedetent 63 defines the position “cover open”; the detent 64 defines theposition “cover closed”. Given employment of identical springs 60 and62, approximately no drive power is needed for moving the tractionmeans. Via the positive lock to the cover devices 16 a and 16 b, theillustrated detents also form the limit detents for the movement of thecover devices 16 a, 16 b.

FIG. 18 shows a further simplification of the arrangement of thetraction means 38. Differing from the exemplary embodiment according toclaim 17, only one spring 70 with detents is provided. With the gascompression spring 54 tensed, the spring 70 is moved back and forthbetween these detents with the traction means 38. The translation of therelatively short stroke of the gas compression spring 54 onto theactuation path for the cover device 16 a and 16 b ensues via thediameter ratio of the drive wheels 72 and 36. By employing a gascompression spring 54 having a relatively short stroke, installationspace is also saved. Due to the symmetrical guidance of the tractionmeans, for example of a chain, it is possible to guide the deflectionroller 56 moved by the gas compression spring 54 nearly free oftransverse forces.

FIG. 19 shows the structure of a locking mechanism in combination withthe gas compression spring 54. The deflection roller 56 has a cross pin74 that is guided in a longitudinal guide 76. When the gas compressionspring 54 is tensed, the cross pin 74 engages into a recess 78 of thedetent pawl 46. The detent pawl 46 has a further recess 80 into which adetent pin 82 of the retainer magnet 50 engages. The detent pawl 46 canbe turned around the rotational axis 84. When the retaining magnet 50which is an electro-magnet is charged with an operating voltage, thenthe detent pawl 46 retains the cross pin 74. The gas compression spring54 remains in its tense condition, given outage of the operatingvoltage, the retaining magnet 50 releases the detent pin 82, so that thedetent pawl 46 can turn around the rotational axis 84. The cross pin 74thereby releases from the recess 78, and the deflection roller 46 movestoward the right in FIG. 19 and drives the traction means. As a resultof suitable lever relationships at the detent pawl 46, even a slightretaining force of the magnets suffices in order to hold the gascompression spring 54 in the tensed condition.

FIG. 20 shows another embodiment of the interlock, whereby the detentpawl 46′ implements a linear, vertical movement along oblong holes 86.The recesses 80 and 78 contain guide bevels 88 and 90 that define theforce equilibrium in the interlocked condition.

FIG. 21 shows a further exemplary embodiment of the interlock mechanismhaving a swivel lever 94 that contains an oblong hole guide 96. In thelocked condition, the retaining magnet 50′ holds the swivel lever 94, towhich an armature plate 92 is secured. The cross pin 74′ of thedeflection roller 56′, a deflection pinion in this case, is guided bothin the longitudinal guide 76′ as well as in the oblong hole guide 96.When the electric retaining magnet 50′ drops off, then the swivel lever94 pivots up until oblong hole guide 96 and longitudinal guide 76′ arecongruent. The cross pin 74 can then move in both guides 79, 76. In thisexemplary embodiment, the electric retaining magnet 50 requires only anextremely low retaining force.

FIG. 22 shows an exemplary embodiment of a safety mechanism with aninterlock on the basis of a swivel lever 94. A chain is provided here asa traction means 38 that is placed on the drive shaft 36 via the pinion.A chain tension spring 100 with damping elements 102 is moved betweentwo limit detents 104. The lever translation of the retaining magnet 50relative to the gas spring 54 is determined by the ratio distance “a” ofthe swivel lever pivot point 106 relative to the axis 108 of the gascompression spring 54 relative to the distance “b” of the swivel pivotpoint 106 from the axis 110 of the retaining magnet 50.

Although other modifications and changes may be suggested by thoseskilled in the art, it is the intention of the inventor to embody withinthe patent warranted hereon all changes and modifications as reasonablyand properly come within the scope of their contribution to the art.

What is claimed is:
 1. A fixing station for fixing toner images on acarrier material which moves passed the fixing station in a movingdirection, comprising; a heating device with at least one radiant heatsource that emits radiation in a direction of the carrier material; acover device movable essentially parallel to the moving direction of thecarrier material and that is moved in to the beam path between said atleast one radiant heat source and the carrier material, given a stop ofthe carrier material the cover device is moved with the velocity VR,according to the relationship: vR=−vP, wherein vP is a transportvelocity of the carrier material, and given continued transport of thecarrier material with the velocity vP the cover device is moved with thevelocity vR, according to the relationship: vR=vP.
 2. A fixing stationaccording to claim 1, wherein said cover device has at least a width ofthe carrier material.
 3. A fixing station according to claim 1, whereinsaid cover device is flexible as viewed in the moving direction of thecarrier material.
 4. A fixing station according to claim 1, wherein thecover device includes a band.
 5. A fixing station according to claim 1,wherein said cover device includes a plurality of strip-shaped lamellaethat form a window blind.
 6. A fixing station according to claim 1,wherein said cover device in one position is wound up in a fashion of awinding.
 7. A fixing station according to claim 1, further comprising:an endless deflection device is arranged around the heating device; andwherein said cover device is moved along the endless deflection device.8. A fixing station according to claim 1, further comprising: adeflection device having a tensing mechanism that keeps said coverdevice in a tensed condition.
 9. A fixing station according to claim 1,wherein said cover device has a length that is adequate to cover anentire radiation of the at least one radiant heat source in a directionof the carrier material.
 10. A fixing station according to claim 1,wherein said cover device includes a rigid plate for covering said atleast one radiant heat source.
 11. A fixing station according to claim1, wherein said at least one radiant heat source has a radiationtemperature in a range from 500° C. through 800° C. and a maximumintensity of radiation lies at a wavelength greater than 2 μm.
 12. Afixing station according to claim 1, wherein said heating device is afirst heating device and said cover device is a first cover device, andfurther comprising: a second heating device having at least one radiantheat source, said first and second heating devices being arranged atboth sides of the carrier material; a second cover device mounted to bemoved into a beam path between said at least one radiant heat source ofsaid second heating device and the carrier material; and a common driveby which said first and second cover devices are moved.
 13. A fixingstation according to claim 12, wherein said first and second heatingdevices are constructed to operate in a printer device or copier devicethat works in duplex printing mode.
 14. A fixing station according toclaim 1, wherein said at least one radiant heat source is selected fromthe group consisting of: a ceramic flat radiator, a crystal radiator anda foil radiator.
 15. A fixing station according to claim 14, furthercomprising: a controller connected so that said at least one radiantheat source is pre-heated.
 16. A fixing station according to claim 15,wherein said controller controls said at least one radiant heat sourceto be pre-heated to a temperature above 200° C.
 17. A fixing stationaccording to claim 16, wherein said controller operates so that atemperature Tm is established in a steady state at the carrier materialgiven an operation of the radiant heat source with nominal power NL; andthe radiant heat source is pre-heated such that a temperature ofapproximately 0.45 Tm is established on the carrier material.
 18. Afixing station according to claim 17, further comprising: a powercontrol that supplies electrical energy to said at least one radiantheat source; in an operating condition with constant printing, the powercontrol sets a power of approximately 80% NL, NL being the nominalpower; in the operating condition with short stoppage of less than 10seconds, the power is to set to 60% through 80% NL; given an operatingcondition with long stoppage of >10 seconds through <5 minutes, a powerof 30% through 60% NL is set; in the operating condition of standby modehaving a waiting time of >5 minutes, a power of less than 30% NL is set;and given the start operating condition, a power of 100% NL is set. 19.A fixing station according to claim 1, further comprising: a temperaturesensor positioned to acquire a temperature on the carrier material; anda controller connected to said temperature sensor so that energysupplied to said at least one radiant heat source is set such that saidat least one radiant heat source lies slightly above a fixingtemperature Tf.
 20. A fixing station according claim 19, wherein thefixing temperature amounts to 0.8×a temperature Tm which is establishedin a steady state at the carrier material given an operation of theradiant heat source with nominal power.
 21. A fixing station accordingto claim 1, wherein each of said at least one radiant heat sources isdivided to a plurality of zones that are respectively separatelysupplied with the electrical energy; and the zones are supplied withelectrical energy dependent on a width of the carrier material.
 22. Afixing station according to claim 21, further comprising: a controllerto control power to said zones opposite which no carrier materialresides so that they are driven with reduced power.
 23. A fixing stationaccording to claim 21, wherein a longitudinal edge of the carriermaterial lies within a first of said plurality of zones. 24.A fixingstation according to claim 21, wherein a plurality of said zones arecombined and driven like a single zone.
 25. A fixing station accordingto claim 21, wherein said heating device is a first heating device andfurther comprising: a second heating device disposed opposite said firstheating device, said first and second heating devices having zones, saidzones residing opposite one another being driven with a same power. 26.A fixing station according to claim 25, wherein said zones residingopposite one another are connected in series.
 27. A fixing stationaccording to claim 21, further comprising: a power control forcontrolling power to said heating device by one of a pulse packetcontrol and a phase control.
 28. A fixing station according to claim 21,further comprising: a temperature regulator connected such that atemperature higher than a fixing temperature is set in zones havingcarrier material and a lower temperature is set in zones without carriermaterial.
 29. A fixing station according to claim 28, wherein saidtemperature regulator performs a temperature regulation only in zoneswith the carrier material.
 30. A fixing station according to claim 1,further comprising: a drive for said cover device; and a safetymechanism that contains an energy store connected to said cover deviceso that given outage of the drive for the cover device energy is takenfrom the energy store with which the cover device is moved by the safetymechanism into a beam path between said at least one radiant heat sourceand the carrier material.
 31. A fixing station according to claim 30,wherein said energy store is a spring energy store.
 32. A fixing stationaccording to claim 30, wherein said energy store is connected to befilled with energy given every closing movement of the cover device. 33.A fixing station according to claim 30, wherein the energy store isfilled once with energy by the drive of the cover device, and furthercomprising: a locking mechanism connected to lock the energy store andto release the energy store given outage of the drive.
 34. A fixingstation according to claim 33, wherein said locking mechanism includesan electromagnet that is permeated by current during normal operation;and said locking mechanism releasing given outage of the current anddrop-off of the electromagnet.
 35. A fixing station according to claim33, wherein said drive for the cover device includes a magnetic couplingthat uncouples the drive given outage of the drive.
 36. A fixing stationaccording to claim 33, further comprising: shock absorbers that dampimpact of the cover devices.
 37. A fixing station according to claim 33,further comprising: a traction element conducted over a deflectionroller.
 38. A fixing station according to claim 37, further comprising:a swivel lever with an oblong hole guide; a retainer magnet which holdsthe swivel lever at its projecting end; a cross pin of the deflectionroller guided in a stationary longitudinal guide and in the oblong holeguide; wherein given a drop-off of the retaining magnet the swivel leveris turned until oblong hole guide and longitudinal guide are alignedwith one another and the cross pin moves in both guides.